Viscous fluid dilution system and method thereof

ABSTRACT

A dilution system for a hydraulic fracturing fluid includes a dilution manifold, a hydration unit configured to provide a source of liquid, a diluent line connecting the hydration unit to the dilution manifold, a diluent flow control valve on the diluent line, a hydration tank configured to hydrate a mixed additive, a gravity-driven viscous fluid line connecting an exit of the hydration tank to the dilution manifold, a viscous fluid flow meter on the viscous fluid line, and a viscous fluid control valve on the viscous fluid line.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims benefit of an earlier filing date from U.S.Non-provisional application Ser. No. 13/911,296, filed on Jun. 6, 2013,the entire disclosure of which is incorporated herein by reference.

BACKGROUND

In the drilling and completion industry, the formation of boreholes forthe purpose of production or injection of fluid is common. The boreholesare used for exploration or extraction of natural resources such ashydrocarbons, oil, gas, water, and alternatively for CO2 sequestration.To increase the production from a borehole, the production zone can befractured to allow the formation fluids to flow more freely from theformation to the borehole. The fracturing operation includes pumpingfluids, such as water, at high pressure and high rate towards theformation to form formation fractures. To retain the fractures in anopen condition after fracturing pressure is removed, the fractures mustbe physically propped open, and therefore the fracturing fluids commonlyinclude solid granular materials, such as sand, generally referred to asproppants.

In addition to proppants and water, other components of the fracturingfluid can include friction reducing additives to allow fracturing fluidsand proppant to be pumped to a target zone at a higher rate and reducedpressure. The treatment design generally requires the fluid to reachmaximum viscosity as it enters the fracture. The requisite viscosity istypically obtained by the gelation of viscosifying polymers and/orsurfactants in the fracturing fluid. Such additives includesynthetically produced and naturally occurring polymers. The selectionof additives is based on a number of factors including the makeup of theformation, formation fluids, pumping configurations, and boreholetemperatures. The additives can be provided as dry powders andsubsequently hydrated at the fracturing site, which saves deliverycosts, reduces cost of mixing slurry, and saves space by reducing afootprint required for the additives at the site.

The art would be receptive to improved apparatus and methods forprocessing fracturing fluid.

BRIEF DESCRIPTION

A dilution system for a hydraulic fracturing fluid, the dilution systemincluding a dilution manifold; a hydration unit configured to provide asource of liquid; a diluent line connecting the hydration unit to thedilution manifold; a diluent flow control valve on the diluent line; ahydration tank configured to hydrate a mixed additive; a gravity-drivenviscous fluid line connecting an exit of the hydration tank to thedilution manifold; a viscous fluid flow meter on the viscous fluid line;and, a viscous fluid control valve on the viscous fluid line.

A method of processing a fracturing fluid, the method includinghydrating a mixed additive within a hydration tank to achieve a viscousfluid; directing the viscous fluid from the hydration tank to a dilutionmanifold via gravity; directing a diluent stream from a hydration unitto the dilution manifold; diluting the viscous fluid with the diluentstream; and, subsequently directing diluted viscous fluid to a blender.

BRIEF DESCRIPTION OF THE DRAWINGS

The following descriptions should not be considered limiting in any way.With reference to the accompanying drawing, like elements are numberedalike:

FIG. 1 shows a diagram of an exemplary embodiment of a viscous fluiddilution system.

DETAILED DESCRIPTION

A detailed description of one or more embodiments of the disclosedapparatus and method are presented herein by way of exemplification andnot limitation with reference to the Figure.

An exemplary embodiment of a viscous fluid dilution system 10 is shownin FIG. 1, and may be incorporated on a trailer for portability orwithin another set up for a processing plant. A fracturing fluid, suchas a friction reducer, linear gel, or another viscous proppanttransporting fluid, is mixed at a rate which enables complete hydrationon-board the viscous fluid dilution system 10. As will be furtherdescribed below, the fracturing fluid may be mixed at a concentrationhigher than that required for the job design, then hydrated, and thensubsequently diluted on-board the trailer of the system 10.

The additives, friction reducers, dry gels, etc. used for the fracturingfluid may be viscosifying agents such as synthetic or natural polymers.Hydratable polymers include those containing one or more functionalgroups, such as a hydroxyl, carboxyl, sulfate, sulfonate, amino or amidogroup. Preferred synthetic and natural polymers include polysaccharides,polyvinyl alcohols, polyacrylates (including the (meth)acrylates),polypyrrolidones, polyacrylamides (including (meth)acrylamides) as wellas 2-acrylamido-2-methylpropane sulfonate and mixtures thereof.

Other suitable polysaccharides and derivatives are those which containone or more monosaccharide units of galactose, fructose, mannose,glucoside, glucose, xylose, arabinose, glucuronic acid and pyranosylsulfate. These include guar gums and derivatives thereof, locust beangum, tara, xanthan, succinoglycan, scleroglucan and carrageenan.

Preferred viscosifying polymers may include crosslinkablepolysaccharides, such as guar gums and derivatives, cellulose, starch,and galactomannan gums. Cellulose and cellulose derivatives includealkylcellulose, hydroxyalkyl cellulose or alkylhydroxyalkyl cellulose,carboxyalkyl cellulose derivatives such as methyl cellulose,hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxybutyl cellulose,hydroxyethylmethyl cellulose, hydroxypropylmethyl cellulose,hydroxybutylmethyl cellulose, methylhydroxyethyl cellulose,methylhydroxypropyl cellulose, ethylhydroxyethyl cellulose,carboxyethylcellulose, carboxymethylcellulose andcarboxymethylhydroxyethyl cellulose.

Specific examples of polysaccharides useful with the present inventioninclude, but are not limited to, guar gum, hydroxypropyl guar,carboxymethylhydroxypropyl guar and known derivatives of these gums.

Exemplary embodiments of the viscous fluid dilution system 10 include ahydration unit 12, water pump 18, flowmeter 22, mixer 20, diluent flowcontrol valve 44, hydration tank 26, flowmeter 36, viscous fluid controlvalve 38, dilution manifold 42, pump 58, flowmeter 60, and proppantblender 56, details of which will be further described as follows.

The system 10 draws liquid (e.g. fresh water) to the pump 18 from thehydration unit 12. The hydration unit 12 includes an input header 14with a plurality of hydration unit valves 16 that connect or disconnectthe input header 14 from a liquid source, such as water tanks (notshown). The pump 18 pressurizes the liquid to the mixer 20. Theflowmeter 22 measures the liquid flow from the pump 18 to the mixer 20along the line 24 to ensure a proper ratio of liquid to additive withinthe mixer 20. A viscosifying additive, friction reducer, dry gel, etc.is added to the mixer 20. The additives, whether natural or syntheticpolymers, may be introduced to the mixer 20 as a dry powder. The mixedadditive and liquid (water), hereinafter “mixed additive,” is thendelivered to the hydration tank 26 for hydration, such as via line 28and into input 30 of the hydration tank 26. The mixed additive may beintroduced at concentrations higher than that required for execution ofa specific fracturing process. The hydration tank 26 provides the mixedadditive with sufficient residence time therein to achieve the requiredlevel of hydration. The hydration tank 26 may include a number of weirstherein (not shown) which provide a tortuous path within the hydrationtank 26 to hydrate the mixed additive in a continuous process andincrease the residency time of the mixed additive prior to exiting thehydration tank 26. The hydration tank 26 includes an exit 32. Once themixed additive is hydrated to a viscous fluid, the viscous fluid exitsthe hydration tank 26 via exit 32 to a viscous fluid line 34. Along theviscous fluid line 34 are the viscous fluid flowmeter 36 and the viscousfluid control valve 38. The viscous fluid flow meter 36 measures theflow rate of the viscous fluid in the viscous fluid line 34 and theviscous fluid control valve 38 throttles the viscous fluid flow toprovide the precise amount of viscous fluid required by job parameters.A diluent line 40, from the hydration unit 12 to the dilution manifold42, directs a stream of diluent (water) to the dilution manifold 42. Thediluent line 40 is separate from the lines 24, 28. The diluent flowcontrol valve 44 is throttled to introduce diluent (water) to thedilution manifold 42. The viscous fluid line 34 sends the proper amountof viscous fluid to the dilution manifold 42 so as to be diluted withdiluent from the dilution line 40 via the viscous fluid flow meter 36,viscous fluid control valve 38, and diluent flow control valve 44.

The dilution manifold 42 may include a dilution manifold header 46 and aplurality of valves 48 that prevent or allow flow from the dilutionmanifold 42 to a blender header 50 which may also include a number ofvalves 52 that prevent or allow flow from the dilution manifold to theblender header 50. An additional valve 54 is provided on the dilutionmanifold header 46 to separate the hydration line 40 from the viscousfluid line 34 as necessary. The diluted viscous fluid within thedilution manifold 42 having the proper ratio of additive to diluentflows into the blender header 50 and is subsequently pumped to theblender 56 using the pump 58. The flowmeter 60 monitors the flow of thediluted viscous fluid in the line 62 between the pump 58 and the blender56 and can be used to determine if the ratio between additive and wateris correct. Thus, by using only two control valves 38, 44 and flow meter36, the viscous fluid dilution system 10 is configured to ratio theviscous fluid with the diluent. The control valves 38, 44 are configuredto adjust the available net positive suction head from the tworeservoirs (the hydration unit 12 and the hydration tank 26) to achievethe proper fluid ratio. While an additional flow meter (not shown) maybe utilized on the diluent line 40, such as between the diluent flowcontrol valve 44 and the hydration unit 12, such an additional flowmeter would be redundant because flowmeter 60 at the blender 56 willdetermine if the proper ratio is being established between the water andthe viscous fluid from the hydration tank 26. That is, it is notnecessary to measure the rate of the diluent stream because only asingle flow component and the total rate need to be measured. In theillustrated embodiment, the single flow component is the flow of viscousfluid in the viscous fluid line 34, and the total rate is the flow rateof the diluted viscous fluid sent to the blender 56 via line 62.

A power source 64 and control system 66 may be further incorporated intothe viscous fluid dilution system 10. The control system 66 may be usedto automate certain procedures within a method of diluting aconcentrated viscous fluid and to operate certain control elements, suchas the valves 38, 44, and monitor certain monitoring elements, such asthe flow meters 34, 60. The control system 66 may be managed or operatedby an operator or configured for automated control, or both. Forexample, an operator may enter the particular ratio of additive to waterrequired for a fracturing fluid to be added to a proppant blender 56,and the control system 66 may then automatically monitor the flow meter36 and flow meter 60 and throttle the control valves 36 and 44 asnecessary to achieve the correct ratio of additive to water within thedilution manifold 42. The control system 66 may further be employed tooperate and/or monitor other features of the dilution system 10including, but not limited to, the pumps 18, 58, mixer 20, flow meter22, valves 16, 48, 52, 54, and blender 56, although these elements mayalso be controlled and/or monitored by an operator as well.

In operation, a concentrated fluid is mixed by the mixer 20 and directedto the hydration tank 26. The hydration tank 26 hydrates theconcentrated fluid to provide a viscous fluid to the viscous fluid line34, which is metered using the control valve 38 and flowmeter 36. Byexample only, a heavy gel 40 lb/1000 gal can be mixed into the hydrationtank 26 at 60 bbl/min. The heavy gel can be subsequently diluted to 24lb/1000 gal at 100 bbl/min at the blender 56. The extra 40 bbl/min flowsthrough the diluent line 40, which serves as a clean water crossover.

As can be readily understood from a review of FIG. 1, the viscous fluidexiting the hydration tank 26 is not pumped to the dilution manifold 42or blender header 50 and an additional pump is not required to meter theviscous fluid. Instead, the viscous fluid is directed to the dilutionmanifold 42 to be subsequently diluted by the added diluent (water) fromdiluent line 40 solely by gravity. That is, energy for the movement ofthe viscous fluid, as well as the diluent, would be solely dependentupon gravity. The absence of a pump eliminates the cost of a pump aswell as the footprint required by a pump. Moreover, the elimination of apump enables the use of shear sensitive polymers within the viscousfluid dilution system 10, such as but not limited to polyacrylamides (apolymer formed from acrylamide sub units), copolymers of acrylamides,and terpolymers of acrylamides, that would otherwise be damaged and/ordeleteriously affected by shear from a pump. The pumpless viscous fluidline has a shear of approximately 200 (l/s) or less from the hydrationtank 26 to the dilution manifold 42 (less than a lower limit of shear ina centrifugal pump) such that the viscous fluid dilution system 10 iscapable of processing such shear sensitive polymers.

While the invention has been described with reference to an exemplaryembodiment or embodiments, it will be understood by those skilled in theart that various changes may be made and equivalents may be substitutedfor elements thereof without departing from the scope of the invention.In addition, many modifications may be made to adapt a particularsituation or material to the teachings of the invention withoutdeparting from the essential scope thereof. Therefore, it is intendedthat the invention not be limited to the particular embodiment disclosedas the best mode contemplated for carrying out this invention, but thatthe invention will include all embodiments falling within the scope ofthe claims. Also, in the drawings and the description, there have beendisclosed exemplary embodiments of the invention and, although specificterms may have been employed, they are unless otherwise stated used in ageneric and descriptive sense only and not for purposes of limitation,the scope of the invention therefore not being so limited. Moreover, theuse of the terms first, second, etc. do not denote any order orimportance, but rather the terms first, second, etc. are used todistinguish one element from another. Furthermore, the use of the termsa, an, etc. do not denote a limitation of quantity, but rather denotethe presence of at least one of the referenced item.

What is claimed is:
 1. A dilution system for a hydraulic fracturingfluid, the dilution system comprising: a dilution manifold; a hydrationunit configured to provide a source of liquid; a diluent line connectingthe hydration unit to the dilution manifold; a diluent flow controlvalve on the diluent line; a hydration tank configured to hydrate amixed additive; a gravity-driven viscous fluid line connecting an exitof the hydration tank to the dilution manifold; a viscous fluid flowmeter on the viscous fluid line; and, a viscous fluid control valve onthe viscous fluid line.
 2. The dilution system of claim 1, wherein theviscous fluid line has a rate of shear of approximately 200 (l/s) orless from the hydration tank to the dilution manifold.
 3. The dilutionsystem of claim 1, wherein the viscous fluid line is pumpless from thehydration tank to the dilution manifold.
 4. The dilution system of claim1, wherein a ratio of diluent to viscous fluid delivered to the dilutionmanifold is managed by the viscous fluid flow meter, the viscous fluidcontrol valve, and the diluent flow control valve.
 5. The dilutionsystem of claim 4, wherein the diluent line is meterless.
 6. Thedilution system of claim 5, further comprising a blender line flow meterconfigured to measure flow from the dilution manifold to a proppantblender.
 7. The dilution system of claim 1, further comprising a mixerconfigured between the hydration unit and the hydration tank, and ahydration line connecting the hydration unit to the mixer, wherein thehydration line is separate from the diluent line.
 8. The dilution systemof claim 7, wherein the hydration tank is configured to enable acontinuous processing of a mixed additive from the mixer, and a hydratedmixed additive is a viscous fluid as it passes through the exit of thehydration tank to the viscous fluid line.
 9. The dilution system ofclaim 7, further comprising a pump directing the liquid from thehydration unit to the mixer on the hydration line.
 10. The dilutionsystem of claim 9, further comprising a flow meter on the hydrationline.
 11. The dilution system of claim 1, wherein the diluent line fromthe hydration unit to the dilution manifold is gravity-driven andpumpless.
 12. The dilution system of claim 1, wherein the dilutionmanifold is fluidically connected to a blender header of a proppantblender, and a pump directs diluted viscous fluid from the dilutionmanifold to the proppant blender.
 13. The dilution system of claim 12,further comprising a blender line flow meter configured to measure flowfrom the dilution manifold to the proppant blender.
 14. The dilutionsystem of claim 12, further comprising a plurality of valves connectingthe dilution manifold to the blender header.
 15. The dilution system ofclaim 1, wherein the dilution manifold includes a dilution manifoldheader and a dilution manifold header valve, the dilution manifoldheader valve configured to separate the diluent line from the viscousfluid line at the dilution manifold header.
 16. The dilution system ofclaim 1, wherein the diluent line is not connected to the hydrationtank.
 17. The dilution system of claim 1, further comprising a mixerconfigured to direct the mixed additive to an input of the hydrationtank through a mixed additive line, wherein the diluent line is notconnected to the mixed additive line.
 18. The dilution system of claim1, wherein the hydration unit includes an input header and a pluralityof hydration unit valves configured to connect or disconnect the inputheader from the source of liquid.
 19. The dilution system of claim 1,wherein the hydration tank is configured to increase a residency time ofthe mixed additive delivered to the hydration tank at an input of thehydration tank before releasing a viscous fluid at the exit of thehydration tank.
 20. The dilution system of claim 1, wherein the diluentline is meterless.